cm - make a space-space contour map


The number of options makes it difficult to give comprehensive examples.
The best scheme is to start off with 'cm ?' and respond to each line.
After a few plots, you should start typing changes to the last plot
without using handhold mode.  eg:

cm vl:10,20		to change the range of integration
cm ir:1.5 ci:		to change to cone interpolation with a radius of
			1.5 min of arc.

cm np:[51,101]		change the grid spacing to 51 in x and 101 in y

cm oc:			Use the last set of contour levels and line types
			which were specified in this stacks file.

Eventually you can type in new maps directly:

cm 10,-10,-8,5,21,14 vl:8,12 ir:1 ci: st:2 		
			If the rel coordinate system is odra-oddec this will 
			map from 10' to -10' in ra and -8' to 5' in dec with 
			a number of points right for observations spaced at 1'.
			The map is smoothed to 1 arcminute using cone 

cm m:"temp,8,12"	make a map of peak temperature between velocities
			8 and 12 km/s. "temp" is a global macro (see 'dm g:').


Cm makes a space-space image in the current relative coordinate system.
The image is put in image 1 and a contour plot is also made.  A FITS file
or tape or a re-plot with different contour steps can be made from image 1.
In most cases the number of spatial points should be chosen so that they
match the location of the observations, although two points per observation
with some smoothing may be useful.


Normally contour maps are made in the current relative coordinate system.  
THIS IS NOT A TRUE PROJECTION.  You may specify a projection in the 'op' 
command.  If the current rel coordinate system has offsets "odra, oddec" 
then you will get an equal area plot in which the size of the ra offset is 
multiplied by the cosine of the local declination and the units will be 
arcmin.  If ra-dec offsets are used (rc r:), then the plot will be a 
coordinate plot with the ra axis scaled so that it is equal area at the 
center of the plot and the units will be total ra and dec in HMS format.  
In the case of galactic and x-y plots there is no equal area scaling.


With bump interpolation (ni:, use the nearest datum) the interpolation 
radius will have to be large enough to include at least one observation per
map point.  For cone interpolation (ci:) it controls the radius of the 
smoothing function (weight ~ 1 - (distance/interp radius)).  In either case 
a large interpolation radius will use a lot of memory for the array of 
lists of scan numbers to be considered for each map point.
Other interpolation types are Bessel (bi:) and Gaussian (gi:). 

For Gaussian interpolation, the input is the full-width at half maximum 
of the Gaussian with which the data are to be smoothed.  The weight for 
any position y with respect to the current position x in any map made with  
Gaussian interpolation is 

	weight(y) = exp((ln(.5)*(d/hwhm)^2);

where d is the the distance between points x and y and hwhm is the half width 
at half max (=0.5*FWHM) of the Gaussian you choose.  Weights are calculated 
for all points within the interpolation radius you choose (ir:). Weights 
for ir > hwhm are, of course, small. If you choose ir << hwhm, or FWHM < the 
data point interval, it reduces to the case of near point interpolate or 
cone interpolate with small radius.

Note that if you are simulating how another telescope would see your data, 
you need to include the correction for the fact that your data are 
sampled with a Gaussian already. Gaussians add in quadrature.


A contour map can be made with any macro which returns some value for
each stack.  (In fact, vl: is just a special case of using the macro "T*dV").
The macro string should be a macro (with any necessary arguments) which is
in the stacks, local or global macro files.  The macro should use the
'v' command to return the value to be plotted.  The macro will be
run on each stack which is used to construct the map and the value
used for that stack will be that given by v.  For examples, type 'dm g: p:'
and look at T*dV, temp, vpek, or tpek.  The latter two apply a Gauss fit 
to the stack first. 


If automatic contour level selection is used, ~10 levels will be
selected using the same algorithm that is used for scaling the axes of
graphs.  The number of levels may be specified with the nl: parameter,
but it is more useful to specify the step size with st:.  sc: (specify
contours) allows you to pick the contour levels and line types in any
way (see the example above for the easiest way to use sc:).  Line types
are explained in the documentation for fl - type 'fl ??' to read it.
The step size and levels you specify with sc: are stored in the
defaults file in the current foreground stacks directory and will
continue to be accessible with the os: or oc: command any later time
that you run comb with that stacks directory.  The contour selection
mode will be remembered during the current execution of comb.

Stack number and center frequency limits can be used to exclude some
stacks in a file from the mapt.

Hatch mark sizes are expressed in the scale of the map's coordinates.
In odra-oddec, a hatch mark size of .5 will be .5'arc long.  

Data whose weight is below acceptable minimums can be rejected
from the map by setting the mwt: variable.  Try values between 0
and a few.  Negative values of mwt are not recommended.

Specifying a label replaces the default label for the current map only.

This document was last updated on Tue Oct 17 16:24:05 EDT 2000 by Marc W. Pound.